There has been known a belt carrying device including an endless belt supported by a plurality of supporting rollers. In the belt carrying device, at least one of the plurality of supporting rollers serves as a driving roller and is rotated. This gives the endless belt a driving force, so that the endless belt is driven and rotated.
Such a belt carrying device is used as a paper carrying unit and/or an intermediate transfer device in an electrophotographic image forming apparatus. The paper carrying unit is a unit for carrying a sheet placed on an endless belt. The intermediate transfer device is a unit that (i) carries out a primary transfer in which a toner image formed on an image carrier such as a photoreceptor onto a belt (an intermediate transfer belt), (ii) carries the toner image thus transferred onto the belt to a predetermined position, and then (iii) carries out a secondary transfer in which the toner image is transferred onto a sheet.
It is preferable that the plurality of supporting rollers provided in the belt carrying device are positioned so as to be completely in parallel with each other. However, it cannot be denied that some errors can be caused in positioning of the plurality of supporting rollers. The endless belt always has some manufacturing errors. It is difficult to manufacture an endless belt having no deviation in peripheral length in a width direction. A meandering phenomenon (belt training deviation) is most likely to occur in which the endless belt, while it is rotating, moves to one side in an axial direction of the supporting rollers, due to the error caused in positioning of the plurality of supporting rollers and/or the deviation in peripheral length of the endless belt.
In view of this, each of Patent Documents 1 and 2 discloses an intermediate transfer device (a belt carrying device) including an endless belt having meandering preventing guides in the vicinity of both ends in a width direction on an inner peripheral side of the endless belt, respectively. Each of the meandering preventing guides (guides for preventing the endless belt from moving to one side) has a rib shape and is provided so as to extend in a rotation direction of the endless belt. In this kind of intermediate transfer device, a meandering preventing guide provided on the endless belt and an end surface (bottom surface) of a supporting roller come into contact with each other. This causes the meandering phenomenon to be suppressed. This makes it possible to prevent the endless belt from coming off the supporting roller even in case of progress in the meandering. The meandering preventing guides also serve as guiding members used when a belt member is attached to the plurality of supporting rollers. As such, the meandering preventing guides make it possible to prevent the belt member from greatly moving to one end in the axial direction of the plurality of supporting rollers when the belt member is put on the plurality of supporting rollers.
The following describes an intermediate transfer device to be provided in an image forming apparatus, with reference to FIG. 7. As illustrated in FIG. 7, an intermediate transfer device 200 includes a supporting roller 201, a shaft 202 for rotatably supporting the supporting roller 201, and an intermediate transfer belt 203, which is an endless belt and is supported by the supporting roller 201.
The supporting roller 201 includes a roller body 201a having a cylindrical shape, and covers (collars) 201b. The covers 201b are fitted to one and the other ends of the roller body 201a, respectively, in an axial direction of the roller body 201a. The intermediate transfer device 200 actually includes a plurality of supporting rollers 201 although FIG. 7 illustrates only one of the plurality of supporting rollers 201.
As illustrated in FIG. 7, the intermediate transfer belt 203 is designed so that the intermediate transfer belt 203 has a width (i.e., a length of the intermediate transfer belt 203 in the axial direction of the supporting roller 201) longer than a length of the supporting roller 201 (i.e., a length of the supporting roller 201 in the axial direction). As illustrated in FIG. 7, the intermediate transfer belt 203 is positioned so as to project from both ends of the supporting roller 201 in the axial direction. Parts of the intermediate transfer belt 203, which project from the both ends of the supporting roller 201 in the axial direction of the supporting roller 201, are referred to as projecting areas 203a. Meandering preventing guides 205 are fixed on inner peripheral surfaces of the intermediate transfer belt 203 in the projecting areas 203a, respectively. In a case where meandering is caused in the intermediate transfer device 200 illustrated in FIG. 7, a cover 201b and a meandering preventing guide 205 come into contact with each other on an end surface of the supporting roller 201, respectively. This causes the meandering to be suppressed.
As illustrated in FIG. 7, the image forming apparatus includes a cleaning blade 204 which is in contact with a surface on an outer peripheral side of the intermediate transfer belt 203. The cleaning blade 204 is a member for cleaning an outer surface of the intermediate transfer belt 203, by scraping off waste such as paper dust, dirt, dust, and/or toner that has not been subjected to the secondary transfer onto a sheet but remains on the intermediate transfer belt 203.
[Patent Document 1]
Japanese Unexamined Patent Publication 2000-112259 (Tokukai 2000-112259, date of publication: Apr. 21, 2000)
[Patent Document 2]
Japanese Unexamined Patent Publication 2007-003933 (Tokukai 2007-003933, date of publication: Jan. 11, 2007)
Since the projecting areas 203a are not directly supported by the supporting roller 201, the projecting areas 203a can have some deflection. Furthermore, as illustrated in FIG. 9, the deflection causes the projecting areas 203a of the intermediate transfer belt 203 to bend somewhat. This gives rise to a situation in which the projecting areas 203a of the intermediate transfer belt 203 is away from the cleaning blade 204. Such a situation can be caused independently of a material of which the intermediate transfer belt 203 is made. In particular, such a situation is significantly caused in a case where the intermediate transfer belt 203 is made of a low shrinkage resin such as polyimide, polyamide-imide, or polycarbonate.
When such a situation is caused, toner remaining on the projecting area 203a cannot be scraped off by the cleaning blade 204 but is allowed to pass through as it is. This is because the projecting areas 203a of the intermediate transfer belt 203 are away from the cleaning blade 204. That is, the remaining toner passes through the space between the cleaning blade 204 and the intermediate transfer belt 203. As illustrated in FIG. 8, This causes the remaining toner to be accumulated in the vicinity of the projecting area 203a of the intermediate transfer belt 203. Furthermore, the remaining toner thus accumulated linearly extends in a carrying direction of the intermediate transfer belt 203, thereby forming a toner stain. This ultimately causes inadequate cleaning.